chapter 22 - electric fields

Chapter 22: ELECTRIC FIELDS

1. An electric eld is most directly related to:

A. the momentum of a test chargeB. the kinetic energy of a test chargeC. the potential energy of a test chargeD. the force acting on a test chargeE. the charge carried by a test charge

ans: D

2. As used in the denition of electric eld, a test charge:

A. has zero chargeB. has charge of magnitude 1CC. has charge of magnitude 1.6 1019 CD. must be an electronE. none of the above

ans: E

3. Experimenter A uses a test charge q0 and experimenter B uses a test charge 2q0 to measurean electric eld produced by stationary charges. A nds a eld that is:

A. the same in both magnitude and direction as the eld found by BB. greater in magnitude than the eld found by BC. less in magnitude than the eld found by BD. opposite in direction to the eld found by BE. either greater or less than the eld found by B, depending on the accelerations of the test

charges

ans: A

4. The units of the electric eld are:

A. N C2B. C/NC. ND. N/C

E. C/m2

ans: D

5. The units of the electric eld are:

A. J/(Cm)B. J/CC. JCD. J/mE. none of these

ans: A

332 Chapter 22: ELECTRIC FIELDS

6. Electric eld lines:

A. are trajectories of a test chargeB. are vectors in the direction of the electric eldC. form closed loopsD. cross each other in the region between two point chargesE. are none of the above

ans: E

7. Two thin spherical shells, one with radius R and the other with radius 2R, surround an isolatedcharged point particle. The ratio of the number of eld lines through the larger sphere to thenumber through the smaller is:

A. 1B. 2C. 4D. 1/2E. 1/4

ans: A

8. A certain physics textbook shows a region of space in which two electric eld lines cross eachother. We conclude that:

A. at least two point charges are presentB. an electrical conductor is presentC. an insulator is presentD. the eld points in two directions at the same placeE. the author made a mistake

ans: E

9. Choose the correct statement concerning electric eld lines:

A. eld lines may crossB. eld lines are close together where the eld is largeC. eld lines point away from a negatively charged particleD. a charged point particle released from rest moves along a eld lineE. none of these are correct

ans: B

10. The diagram shows the electric eld lines due to two charged parallel metal plates. We concludethat:

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X

Y Z

A. the upper plate is positive and the lower plate is negativeB. a proton at X would experience the same force if it were placed at YC. a proton at X experiences a greater force than if it were placed at ZD. a proton at X experiences less force than if it were placed at ZE. an electron at X could have its weight balanced by the electrical force

ans: B

Chapter 22: ELECTRIC FIELDS 333

11. Let k denote 1/4$60. The magnitude of the electric eld at a distance r from an isolated pointparticle with charge q is:

A. kq/rB. kr/qC. kq/r3

D. kq/r2

E. kq2/r2

ans: D

12. The diagram shows the electric eld lines in a region of space containing two small chargedspheres (Y and Z). Then:

X

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A. Y is negative and Z is positiveB. the magnitude of the electric eld is the same everywhereC. the electric eld is strongest midway between Y and ZD. the electric eld is not zero anywhere (except innitely far from the spheres)E. Y and Z must have the same sign

ans: D

13. The diagram shows the electric eld lines in a region of space containing two small chargedspheres (Y and Z). Then:

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A. Y is negative and Z is positiveB. the magnitude of the electric eld is the same everywhereC. the electric eld is strongest midway between Y and ZD. Y is positive and Z is negativeE. Y and Z must have the same sign

ans: D


14. The electric eld at a distance of 10 cm from an isolated point particle with a charge of 2109 Cis:

A. 1.8N/CB. 180N/CC. 18N/CD. 1800N/CE. none of these

ans: D

15. An isolated charged point particle produces an electric eld with magnitude E at a point 2maway from the charge. A point at which the eld magnitude is E/4 is:

A. 1m away from the particleB. 0.5m away from the particleC. 2m away from the particleD. 4m away from the particleE. 8m away from the particle

ans: D

16. An isolated charged point particle produces an electric eld with magnitude E at a point 2maway. At a point 1m from the particle the magnitude of the eld is:

A. EB. 2EC. 4ED. E/2E. E/4

ans: C

17. Two protons (p1 and p2) are on the x axis, as shown below. The directions of the electric eldat points 1, 2, and 3, respectively, are:

p1 p2

1 2 3

A. , , B. , , C. , , D. , , E. , ,

ans: E


18. Two point particles, with a charges of q1 and q2, are placed a distance r apart. The electric eldis zero at a point P between the particles on the line segment connecting them. We concludethat:

A. q1 and q2 must have the same magnitude and signB. P must be midway between the particlesC. q1 and q2 must have the same sign but may have dierent magnitudesD. q1 and q2 must have equal magnitudes and opposite signsE. q1 and q2 must have opposite signs and may have dierent magnitudes

ans: C

19. The diagrams below depict four dierent charge distributions. The charge particles are all thesame distance from the origin. The electric eld at the origin:

2q 3q

5q

1

3q 3q

5q

2

2q 2q

5q

5q

3

2q 2q

5q

5q

4

A. is greatest for situation 1B. is greatest for situation 3C. is zero for situation 4D. is downward for situation 1E. is downward for situation 3

ans: C

20. The diagram shows a particle with positive charge Q and a particle with negative charge Q.The electric eld at point P on the perpendicular bisector of the line joining them is:

+Q

Q

P

A. B. C. D.

E. zero

ans: A


21. The diagram shows two identical particles, each with positive charge Q. The electric eld atpoint P on the perpendicular bisector of the line joining them is:

+Q

+Q

P

A. B. C. D.

E. zero

ans: C

22. Two point particles, one with charge +8 109 C and the other with charge 2 109 C, areseparated by 4m. The electric eld in N/C midway between them is:

A. 9 109B. 13, 500C. 135, 000D. 36 109E. 22.5

ans: E

23. Two charged point particles are located at two vertices of an equilateral triangle and the electriceld is zero at the third vertex. We conclude:

A. the two particles have charges with opposite signs and the same magnitudeB. the two particles have charges with opposite signs and dierent magnitudesC. the two particles have identical chargesD. the two particles have charges with the same sign but dierent magnitudesE. at least one other charged particle is present

ans: E

24. Two point particles, with the same charge, are located at two vertices of an equilateral triangle.A third charged particle is placed so the electric eld at the third vertex is zero. The thirdparticle must:

A. be on the perpendicular bisector of the line joining the rst two chargesB. be on the line joining the rst two chargesC. have the same charge as the rst two particlesD. have charge of the same magnitude as the rst two charges but its charge may have a

dierent signE. be at the center of the triangle

ans: A


25. Positive charge Q is uniformly distributed on a semicircular rod. What is the direction of theelectric eld at point P, the center of the semicircle?

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PQ

A. B. C.

D. E. c

ans: D

26. Positive charge +Q is uniformly distributed on the upper half a semicircular rod and negativecharge Q is uniformly distributed on the lower half. What is the direction of the electric eldat point P, the center of the semicircle?

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........ P

+Q

Q

A. B. C.

D. E. c

ans: B

27. Positive charge +Q is uniformly distributed on the upper half a rod and negative charge Qis uniformly distributed on the lower half. What is the direction of the electric eld at pointP, on the perpendicular bisector of the rod?

P+Q

Q

A. B. C.

D. E. c

ans: B


28. The electric eld due to a uniform distribution of charge on a spherical shell is zero:

A. everywhereB. nowhereC. only at the center of the shellD. only inside the shellE. only outside the shell

ans: D

29. A charged particle is placed in an electric eld that varies with location. No force is exertedon this charge:

A. at locations where the electric eld is zeroB. at locations where the electric eld strength is 1/(1.6 1019)N/CC. if the particle is moving along a eld lineD. if the particle is moving perpendicularly to a eld lineE. if the eld is caused by an equal amount of positive and negative charge

ans: A

30. The magnitude of the force of a 400-N/C electric eld on a 0.02-C point charge is:

A. 8.0NB. 8 105NC. 8 103ND. 0.08NE. 2 1011N

ans: A

31. A 200-N/C electric eld is in the positive x direction. The force on an electron in this eld is:

A. 200N in the positive x directionB. 200N in the negative x directionC. 3.2 1017 N in the positive x directionD. 3.2 1017 N in the negative x directionE. 0

ans: D

32. An electron traveling north enters a region where the electric eld is uniform and points north.The electron:

A. speeds upB. slows downC. veers eastD. veers westE. continues with the same speed in the same direction

ans: B


33. An electron traveling north enters a region where the electric eld is uniform and points west.The electron:

A. speeds upB. slows downC. veers eastD. veers westE. continues with the same speed in the same direction

ans: C

34. Two charged particles are arranged as shown. In which region could a third particle, withcharge +1C, be placed so that the net electrostatic force on it is zero?

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I II III

2C 4C

A. I onlyB. I and II onlyC. lII onlyD. I and III onlyE. II only

ans: A

35. An electric dipole consists of a particle with a charge of +6106 C at the origin and a particlewith a charge of 6 106 C on the x axis at x = 3 103m. Its dipole moment is:A. 1.8 108 C m, in the positive x directionB. 1.8 108 C m, in the negative x directionC. 0 because the net charge is 0D. 1.8 108 C m, in the positive y directionE. 1.8 108 C m, in the negative y direction

ans: B

36. The force exerted by a uniform electric eld on a dipole is:

A. parallel to the dipole momentB. perpendicular to the dipole momentC. parallel to the electric eldD. perpendicular to the electric eldE. none of the above

ans: E

37. An electric eld exerts a torque on a dipole only if:

A. the eld is parallel to the dipole momentB. the eld is not parallel to the dipole momentC. the eld is perpendicular to the dipole momentD. the eld is not perpendicular to the dipole momentE. the eld is uniform

ans: B


38. The torque exerted by an electric eld on a dipole is:

A. parallel to the eld and perpendicular to the dipole momentB. parallel to both the eld and dipole momentC. perpendicular to both the eld and dipole momentD. parallel to the dipole moment and perpendicular to the eldE. not related to the directions of the eld and dipole moment

ans: C

39. The diagrams show four possible orientations of an electric dipole in a uniform electric eld nE.Rank them according to the magnitude of the torque exerted on the dipole by the eld, leastto greatest.

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np

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4A. 1, 2, 3, 4B. 4, 3, 2, 1C. 1, 2, 4, 3D. 3, 2 and 4 tie, then 1E. 1, 2 and 4 tie, then 3

ans: E

40. A uniform electric eld of 300N/C makes an angle of 25H with the dipole moment of an electricdipole. If the torque exerted by the eld has a magnitude of 2.5107N m, the dipole momentmust be:

A. 8.3 1010 C mB. 9.2 1010 C mC. 2.0 109 C mD. 8.3 105 C mE. 1.8 104 C m

ans: C

41. When the dipole moment of a dipole in a uniform electric eld rotates to become more nearlyaligned with the eld:

A. the eld does positive work and the potential energy increasesB. the eld does positive work and the potential energy decreasesC. the eld does negative work and the potential energy increasesD. the eld does negative work and the potential energy decreasesE. the eld does no work

ans: B


42. The dipole moment of a dipole in a 300-N/C electric eld is initially perpendicular to the eld,but it rotates so it is in the same direction as the eld. If the moment has a magnitude of2 109 C m, the work done by the eld is:A. 12 107 JB. 6 107 JC. 0D. 6 107 JE. 12 107 J

ans: D

43. An electric dipole is oriented parallel to a uniform electric eld, as shown.

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nEnp

It is rotated to one of the ve orientations shown below. Rank the nal orientations accordingto the change in the potential energy of the dipole-eld system, most negative to most positive.

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3

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nEnp

4A. 1, 2, 3, 4B. 4, 3, 2, 1C. 1, 2, 4, 3D. 3, 2 and 4 tie, then 1E. 1, 2 and 4 tie, then 3

ans: A

44. The purpose of Millikens oil drop experiment was to determine:

A. the mass of an electronB. the charge of an electronC. the ratio of charge to mass for an electronD. the sign of the charge on an electronE. viscosity

ans: B

45. A charged oil drop with a mass of 2 104 kg is held suspended by a downward electric eldof 300N/C. The charge on the drop is:

A. +1.5 106 CB. 1.5 106 CC. +6.5 106 CD. 6.5 106 CE. 0

ans: D


chapter 22 - electric fields

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